Agrobacterium rhizogenes is a soil bacterium that uses a natural system of genetic transformation to insert R.sub.i T-DNA into the genome of dicotyledonous plants. R.sub.i T-DNA is composed of TL (left) and TR (right) segments. D. Tepfer, "Transformation of Several Species of Higher Plants by Agrobacterium Rhizogenes: Sexual Transmission of the Transformed Genotype and Phenotype", Cell, 37:959-967 (1984).
The presence of the R.sub.i T-DNA causes the formation of genetically transformed roots which can give rise to whole plants carrying foreign genes. The transformed roots are genetically stable and easy to manipulate. P. Guerche et al., "Genetic Transformation of Oil Seed Rape (Brassica napas) by the R.sub.i T-DNA of Agrobacterium rhizogenes and Analysis of inheritance of the transformed phenotype", Mol. Gen. Gent. 206:382-386 (1987), hereby incorporated by reference. The roots are characterized by rapid growth, altered geotropic behavior, and a high degree of branching. Apical dominance is reduced, more laterals form and the general propensity to differentiate root meristems is increased, and morphological plasticity is augmented. D. Tepfer, "R.sub.i T-DNA from Agrobacterium rhizogenes, A Semichemical That Alters Morphological Plasticity", Plant Molecular Biology; pgs. 565-571 (1987), hereby incorporated by reference.
The genetically transformed roots, in many species, give rise to whole plants carrying the T-DNA genes. Such whole plants exhibit a transformed phenotype which includes increased branching, shortened stature, wrinkled leaves, modified flowering, annualism in biennials, and more branched root systems. C. Lambert and D. Tepfer, "Use of Agrobacterium rhizogenes to create trangenic apple trees having an altered organogenic response to hormones", Theor. Appl. Genet. 85:105-109 (1992). A good description of the transformed phenotype can be found in D. Tepfer, "R.sub.i T-DNA from Agrobacterium rhizogenes, A Semichemical That Alters Morphological Plasticity", Plant Molecular Biology; pgs. 565-571 (1987). In addition, in the axenic root cultures of Calystegia sepium and Atropa belladonna, genetic transformation by R.sub.i T-DNA increases biomass and tropane alkaloid production. See G. Jung and D. Tepfer, "Use of Genetic Transformation by the R.sub.i T-DNA of Agrobacterium rhizogenes to Stimulate Biomass and Tropane Alkaloid Production in Atropia Belladonna and Calystegia Sepium Roots Grown In Vitro", Plant Science, 50:145-151 (1987) .
It is known that R.sub.i TR-DNA carries genes responsible for auxin and opine synthesis. R.sub.i TL-DNA carries genes that alter development and phenotype. R.sub.i TL-DNA is known to induce the following developmental and phenotypic changes: reduced apical dominance, shortened internodes, root plagiotropism, partial sterility, annualism in biennials and leaf wrinkling. See Li-Yuan Sun et al., "Modification of phenotype in Belgian endive (Cichorium intybus) through genetic transformation by Agrobacterium rhizogenes: conversion from biennial to annual flowering", Trangenic Research 1:14-22 (1992) and Li-Yuan Sun et al., "Changes in flowering and the accumulation of polyamines and hydroxycinnamic acid-polyamine conjugates in tobacco plants transformed by the rol A locus from the R.sub.i TL-DNA of Agrobacterium rhizogenes", Plant Science 80:145-56 (1991).
R.sub.i TL-DNA has been sequenced and contains 18 stretches of DNA sequences that do not contain any stop condons. (Such areas are referred to as an open reading frame.) The 18 stretches of DNA sequences encode putative proteins of 100 amino acids or more. Through the use of insertional mutagenesis, some of the open reading frames have been recognized as being important in root induction. These are the "rol" (root locus) genes, which are designated A-D. F. White, B. Taylor, G. Huffman, M. Gordon and E. Nester, "Molecular and genetic analysis of the transferred DNA regions of the root inducing plasmid of Agrobacterium rhizogenes," J. Baceriol., 164 (1985) 33-44. In experiments conducted with tobacco, it was discovered that the dwarfing of aerial parts can generally be assigned to both rol A and rol C; wrinkled leaves are primarily due to rol A; and reduced apical dominance is due to rol C. D. Tepfer et al., "Control of Root System Architecture Through Chemical and Genetic Alterations of Polyamine Metabolism", Biology of Adventitious Root Formation, pgs. 181-189 (1994); see also Li-Yuan Sun et al., "Changes in flowering and the accumulation of polyamines and hydroxycinnamic acid-polyamine conjugates in tobacco plants transformed by the rol A locus from the R.sub.i TL-DNA of Agrobacterium rhizogenes", Plant Science 80:145-156 (1991). T. Schmulling, J. Schell and A. Spena, "Single genes from Agrobacterium rhizogenes influence plant development," EMBO J., 7 (1988) 2621-2629; V. Sinkar, F. Pythoud, F. White, E. Nester and M. Gordon, "rol locus of the Ri plasmid directs developmental abnormalities in transgenic plants," Genes and Dev., 2 (1988) 688-698; V. Sinkar, F. White, I. Furner, M. Abrahamsen, F. Pythoud and M. Gordon, "Reversion of aberrant plants transformed with Agrobacterium rhizogens is associated with the transcriptional inactivation of the TL-DNA genes", Plant Physiol., 86 (1988) 47-57.
Ornamental plants such as geraniums and scented geraniums decorate gardens and balconies where they provide a diverse spectrum of fragrance. The scents of the leaves range anywhere from lime and lemon to strawberry, peach, coconut, and rose. The scent originates from oils released by glands on the leaves.
While scented geraniums produce pleasant fragrances, the plants otherwise have rather unpleasant ornamental characteristics, such as an unattractive plant habit. It is therefore the principal object of this invention to provide genetically transformed geraniums having improved ornamental characteristics.